must be <a href="#Uniqueness_of_identifiers">unique</a>.
If absent, each type stands for one item of that type.
Parameter and result
lists are always parenthesized except that if there is exactly
one unnamed result it may be written as an unparenthesized type.
</p>

<p>
The final incoming parameter in a function signature may have
a type prefixed with <code>...</code>.

     the reduction axis labels.

 (c) Batch Dimensions: Axes corresponding to labels appearing in each of the
     input subscripts and also in the output subscript make up the batch
     dimensions in Tensor contraction. Unnamed axis labels corresponding to
     ellipsis (`...`) also correspond to batch dimensions.
     For example, for the equation denoting batch matrix multiplication,